An increasing variety of lighting applications require a precisely controlled spectral characteristic of the radiant electromagnetic energy. It has long been known that combining the light of one color with the light of another color creates a third color. For example, the commonly used primary colors Red, Green and Blue of different amounts can be combined to produce almost any color in the visible spectrum. Adjustment of the amount of each primary color enables adjustment of the spectral properties of the combined light stream. Recent developments for selectable color systems have utilized solid state devices, such as light emitting diodes, as the sources of the different light colors.
Light emitting diodes (LEDs) were originally developed to provide visible indicators and information displays. For such luminance applications, the LEDs emitted relatively low power. However, in recent years, improved LEDs have become available that produce relatively high intensities of output light. These higher power LEDs, for example, have been used in arrays for traffic lights. Today, LEDs are available in almost any color in the color spectrum.
Systems are known which combine controlled amounts of projected light from at least two LEDs of different primary colors. Attention is directed, for example, to U.S. Pat. Nos. 6,459,919, 6,166,496 and 6,150,774. Typically, such systems have relied on using pulse-width modulation or other modulation of the LED driver signals to adjust the intensity of each LED color output. Such prior systems have relied on direct radiation or illumination from the individual source LEDs.
In some applications, the LEDs may represent undesirably bright sources if viewed directly. Solid state light emitting elements have small emission output areas and typically they appear as small point sources of light. As the output power of solid state light emitting elements increases, the intensity provided over such a small output area represents a potentially hazardous light source. Increasingly, direct observation of such sources, particularly for any substantial period of time, may cause eye injury.
Also, the direct illumination from LEDs providing multiple colors of light has not provided optimum combination throughout the field of illumination. Pixelation often is a problem with prior solid state lighting devices. In some systems, the observer can see the separate red, green and blue lights from the LEDs at short distances from the fixture, even if the LEDs are covered by a translucent diffuser. The light output from individual LEDs or the like appear as identifiable/individual point sources or ‘pixels.’ Integration of colors by the eye becomes effective only at longer distances, otherwise the fixture output exhibits striations of different colors.
Another problem arises from long-term use of LED type light sources. As the LEDs age, the output intensity for a given input level of the LED drive current decreases. As a result, it may be necessary to increase power to an LED to maintain a desired output level. This increases power consumption. In some cases, the circuitry may not be able to provide enough light to maintain the desired light output level. As performance of the LEDs of different colors declines differently with age (e.g. due to differences in usage), it may be difficult to maintain desired relative output levels and therefore difficult to maintain the desired spectral characteristics of the combined output. The output levels of LEDs also vary with actual temperature (thermal) that may be caused by difference in ambient conditions or different operational heating and/or cooling of different LEDs. Temperature induced changes in performance cause changes in the spectrum of light output.
U.S. Pat. No. 5,803,592 suggests a light source design intended to produce a high uniformity substantially Lambertian output. The disclosed light design used a diffusely reflective hemispherical first reflector and a diffuser. The light did not use a solid state type light emitting element. The light source was an arc lamp, metal halide lamp or filament lamp. The light included a second reflector in close proximity to the lamp (well within the volume enclosed by the hemispherical first reflector and the diffuser) to block direct illumination of and through the diffuser by the light emitting element, that is to say, so as to reduce the apparent surface brightness of the center of the light output that would otherwise result from direct output from the source.
U.S. Pat. No. 6,007,225 to Ramer et al. (Assigned to Advanced Optical Technologies, L.L.C.) discloses a directed lighting system utilizing a conical light deflector. At least a portion of the interior surface of the conical deflector has a specular reflectivity. In several disclosed embodiments, the source is coupled to an optical integrating cavity; and an outlet aperture is coupled to the narrow end of the conical light deflector. This patented lighting system provides relatively uniform light intensity and efficient distribution of light over a field of illumination defined by the angle and distal edge of the deflector. However, this patent does not discuss particular color combinations or effects or address specific issues related to lighting using one or more solid state light emitting elements.
Hence, a need still exists for a technique to efficiently process electromagnetic energy from one or more solid state light emitting sources and direct uniform electromagnetic energy effectively toward a desired field of illumination, in a manner that addresses as many of the above discussed issues as practical.
Also, there are a variety of consumer needs and applications that require additional intelligence in association with lighting equipment. It is often desirable to provide enhanced control features for the light and/or for associated equipment, either in the form of wireless remote control or in response to occupancy detection.
A variety of technologies are known, for example based on ultrasonic sensing and passive or active sensing, to determine occupancy of an area to be illuminated and control one or more light fixtures in response to the occupancy determination. Typically, the occupancy sensor is mounted in a wall or ceiling of the area that the lighting device is intended to illuminate. Such control based on sensing of occupancy reduces energy and maintenance costs by turning-off the light(s) when not needed. Typically, existing occupancy sensors have been used with conventional lighting devices, such as fluorescent and incandescent lamps. General strategies of occupancy responsive control may be applicable to LED based lighting, but systems and methodologies have not yet been developed that specifically integrate such control strategies into LED based lighting in a highly effective and efficient manner.
Hence, it would also be desirable that solid state lighting solutions also support enhanced sensing and processing capabilities for communication purposes, automation and control of the lighting equipment and/or other systems, monitoring, or the like.